Van Eyck is considered one of the greatest painters of any period. Advances in oil techniques helped him paint the physical world in minute detail and with a degree of realism never before possible. It was said he knew fabrics like a weaver, buildings like an architect, and plants like a botanist. Here it is hard to believe that the angel's gleaming brocade is yellow pigment, not true gold, "woven" with brushstrokes, not threads.

In this painting Gabriel announces to Mary that she will bear the son of God. She modestly draws back and responds, "Behold the handmaiden of the Lord." Her words are printed upside down for the Lord above to see. The Holy Spirit descends to her on seven rays of light. This is the moment God's plan for salvation is set in motion. Through Christ's human incarnation the old era of the Law is transformed into a new era of Grace.

Almost every element in the painting contributes to this theme. The architecture moves from older, round Romanesque forms to pointed Gothic arches. In the floor tiles, scenes from the Old Testament prefigure New Testament events; David's slaying of Goliath, for example, fore tends Christ's triumph over the devil. The single top window, where Jehovah stands, contrasts the triple windows below, which suggest the Christian trinity. Even Mary's overlarge figure inside the chapel operates symbolically to underscore her identification with the Church. The lilies beside her refer to her purity.